Things to Consider
Several things came to mind when designing BAFS:
I only have 1 printer, Anet A8v2, so should making this will need to comply with the printer's limitation. That is it only have 4 extra pins and I have used 3 (see my post about this). So BAFS must only use 1 pin.
It must be as simple as possible so even a beginner can make it. I am a beginner after all, I can't make a complicated stuffs anyway.
It must be as cheap as possible so anyone can make it without spending a lot of money. For me, it just doesn't make any sense to have expensive addon while having cheap printer.
It must use a commonly available parts so anyone doesn't have to order parts from the other side of the world. I live in a place where 3d printers are not that popular, so some parts are hard to get, even if it's available, it's expensive.
It should be modular so if anyone want to try it, they can start with just two filaments without building something big.
Anet A8v2 has a thin frame, so it must be as light as possible.
There are already available addons for multi color printing, some have similar principle, so BAFS wil have similar problems too. Well, if I can make something that even remotely similar to those then it's already an achievement.
The Design
As I have mentioned in my previous post, the concept is simple, just add a shaft, more gears, and more arms, in other word, multiply it.
Commonly Available and Affordable Parts
Basic working principle of a 3d printer's extruder in common people language is pinching filament between a gear driven by a motor and something, an idler or another gear so when the motor rotates the filament also moves.
So there are 4 main parts, the motor, the gear, the idler and the shaft.
Long shafts are easy to get every where, for this purpose it's the same diameter as the motor shaft, 5mm. For the length, it will be decided later. The main problem with buying long shaft is often it get bent during delivery. I got mine bent so bad, 1 bought 50 cm, I can only use about 20cm of it.
The gear and idler are the same with stock A8v2, fortunately it uses commonly available here where I live. You could use another as long as its bore is 5mm for the gear and 3mm for the idler. Although for the idler you need to consider more things. I will explain it later. The point is both the gear and idler are easy to get, and if you're not using branded ones, they're already cheap. I can't say much if you live where it's hard to get.
The simples way to have multi color 3d printing is to just add more extruders meaning more motors, but I can't do that because my A8v2 only has 1 pin left, and stepper motors are expensive. I could use second hand motors but there are another things to consider.
The commonly available stepper motors are heavy, there's a pancake version, or even the smaller ones like 28BYJ-48 but you still need a driver to use stepper motors, which needs at least 3 pins (enable, step and direction pin) for each motor. There may be a way around it, I don't know, for me, at least with my current knowledge and ability, using stepper motors are too complicated for the purpose.
So, this approach won't do for me.
And then there are things called hobby servos. There are many kind of hobby servos, cheap and expensive, big and small, original and clones. We'll be using the cheap ones.
It's cheaper and lighter. A common stepper motor weight about a quarter of a kilogram, a servo weights about 50 grams.
Also it only needs one pin to control a servo motor.
But we need more than 1 servo motor? Yes, that's where the interesting things come to play. We'll be using 1 servo motor for each extruder with the help of an additional microcontroller.
The printer only need to provide 1 pin, and it will be connected to the microcontroller.
Well, that's it for now. I will explain more on part 2.